Our long-term goal is to understand the physiological and pathophysiological role of the BK-type voltage and Ca2+-activated K+ channels. BK channels modulate physiological processes that involve Ca2+ signaling in many tissues, such as muscle contraction, renal function and neural transmission. These channels are composed of the pore-forming, voltage- and Ca2+ -sensing a subunit that is encoded by a single Slo1 gene and four types of auxiliary subunit (1-4). Each of these subunits modulates functional properties of the Slo1 channel with distinct characteristics and tissue-specific expression. Thus, subunits help to define the phenotypes and physiological roles of BK channels in various tissues. To achieve our long-term goal, it is necessary to study the molecular mechanism of the interaction between Slo1 and the subunits. Previous publications and our preliminary data demonstrate that, although all four types of subunit share similar structural features, the mechanisms of their modulation of Slo1 channels differ in two key aspects: 1) they target different molecular components and processes in Slo1 that are important in channel gating, and 2) they have different amino acids or motifs (active sites) that are critical for altering gating of Slo1 channels. Based on these preliminary results, we will use the methods of electrophysiology, mutagenesis, chemical modification and kinetic modeling to achieve the following specific aims: I. To identify the molecular targets of subunits modulation in Slo1 channels. II. To identify the active sites of subunits. III. To examine if subunits affect the interaction between the membrane-spanning and the cytosolic domains that is critical for BK channel gating. Aim III will establish a link between the subunit association, as studied in Aims I and II, with a structural mechanism of BK channel gating that has been revealed recently. This study will identify amino acids and structural motifs important for BK channel gating and reveal the nature of the interactions between Slo1 and subunits. It will lay the foundation for understanding the molecular basis of BK channel related pathological conditions, such as epilepsy and hypertension, and provide the target and rationale for their treatment. subunits of K+ channels with transmembrane segment, such as the KCNE family and BK subunits modulate the gating properties of their respective a subunits, which are key to the physiological roles of these channels. Our preliminary studies suggest that some of these subunits may affect channel gating through common mechanisms. Therefore, this study will provide insights to these common mechanisms of K+ channel function.